1. Field of the Invention
The present invention relates to a display, and more specifically, it relates to a display including an emission layer such as an organic layer.
2. Description of the Background Art
Requirement for flat display devices exhibiting smaller power consumption than a generally employed CRT is recently increased following diversification of information apparatuses. Among such flat display devices, a display employing an organic electroluminescence element (hereinafter referred to as an organic EL element) characterized by high efficiency, thinness/lightweight property and no view angle dependency is actively researched and developed.
FIG. 12 is a perspective view showing the overall structure of a conventional organic EL display. FIG. 13 is a plan view of the conventional organic EL display shown in FIG. 12. Referring to FIGS. 12 and 13, anodes 102 of ITO (indium-tin oxide) are formed on a glass substrate 101 in the conventional organic EL display. Organic layers 105 including hole injection layers, hole transport layers and emission layers are formed on the anodes 102. A cathode 103 is formed on the organic layers 105. This cathode 103 is provided with an outlet terminal 104.
Drive circuits 106a and 106b are formed on the glass substrate 101. Video signal lines 151 are connected to the drive circuit 106a. Scanning lines 152 and power supply lines 153 are connected to the drive circuit 106b. The outlet terminal 104 of the cathode 103 is connected to a current supply input terminal 108 for supplying current from a current source. The cathode 103 is formed to cover a plurality of pixels. Therefore, current for driving the plurality of pixels concentrically flows into the cathode 103.
As hereinabove described, the current for driving the plurality of pixels flows into the cathode 103 in the conventional organic EL display. In this case, the current concentrates to the outlet terminal 104 of the cathode 103, disadvantageously leading to resistance heating of the outlet terminal 104. Particularly when the organic EL display is increased in size, large current flows to the outlet terminal 104 to increase resistance heating thereof.
When resistance heating of the outlet terminal 104 is increased, the temperature of the cathode 103 is increased to disadvantageously deteriorate the organic layers 105 located under the cathode 103.
In general, therefore, various methods are proposed in order to suppress heat generation in an outlet terminal part. For example, Japanese Patent Laying-Open No. 2001-109398 proposes a structure increasing the width of an outlet terminal part.
Even if the width of a single outlet terminal part is increased, however, large current concentrically flows to the single outlet terminal part when the display is increased in size, and hence it is difficult to reduce the quantity of heat generation in the outlet terminal part. When the display is increased in size, therefore, it is so difficult to reduce temperature rise of a cathode that it is also difficult to prevent organic layers from deterioration resulting from temperature rise of the cathode.
Japanese Patent Laying-Open No. 2001-85158 discloses a technique of increasing the width of outlet terminal (drawing terminal) parts of a cathode (second electrode) while providing the outlet terminal parts on two portions of opposite edges. In general, however, connection with an external current source is performed on a single portion and hence it is difficult to connect the outlet terminals of the cathode (second electrode) with the external current source when the outlet terminals are provided on two portions of the opposite edges. In the structure disclosed in the aforementioned gazette, further, current can be dispersed to the two outlet terminals (two directions) of the cathode. However, it is difficult to disperse the current in three or four directions. When large current flows in a display increased in size, therefore, it is difficult to disperse the current for inhibiting the cathode from heat generation.